1. Field of the Invention
The present invention relates to an appliance for fixing the proximal end terminal of an electrode cable to a connector member of an implantable medical device, e.g. a heart stimulator, such as a pacemaker or a defibrillator. More particularly, the appliance of the present invention is of the type having a connector insert having a hole for receiving the terminal, and a member for clamping the terminal to fix it in the insert, the clamping member being axially movable in a shaft in the insert which adjoins and crosses said hole, wherein the clamping member has the shape of an unthreaded pin which is held in the shaft so as to be movable axially within limits in the shaft and biased by a spring toward a position therein such that an inner end of the pin is capable of engaging a side of the terminal being exposed in the shaft, the inner end of the pin having a diametrically extending recess to be aligned with the terminal during insertion thereof into the hole.
2. Description of the Prior Art
In a most general and simple type of lead appliance, fixing, the proximal terminal of the electrode cable is axially fixed in the connector member by means of a set screw, which is screwed into a transverse threaded shaft in order to radially press the electrode terminal against contact surfaces of the connector member to thereby achieve fixing of the terminal by clamping. The use of screws requires accurate assembly instructions and a precise tightening torque to be applied to the screw.
Various kinds of screwless electrode fixing devices have been developed. For example, U.S. Pat. No. 4,860,750 discloses a wedge element for fixing a lead in an asymmetrical manner which does not ensure a constant clamping force within the tolerance range of the lead. Also, achievement of safe body fluid sealing of the wedge element requires careful efforts.
U.S. Pat. No. 4,848,346 discloses two circular springs which could be expanded to allow insertion of a heart lead by depressing a straight end portion of the springs protruding from the outer surface of the connector block. However, such protruding end portions may cause unintentional release of the heart lead.
U.S. Pat. No. 6,112,120 discloses an apparatus for connecting a bipolar proximal end terminal of an electrode cable to a connector member of an implantable medical device. The apparatus has two connection outputs, each having a spring-biased electrical contact element exerting a radial pressure on a respective terminal portion. The terminal is fixed in the medical device by means of a separate locking wedge.
An object of the present invention is to provide an improved electrode terminal fixing appliance having an unthreaded fixation pin which is capable of safely snap-lock the terminal in the connector insert only by turning the pin a quarter of a revolution. This object is achieved in an appliance of the type initially described wherein the inner end of the pin has two diametrically aligned depressions at a right angle to the recess, the depressions having a smaller depth than the recess so that the pin is capable of fixing the terminal by clamping action after rotating the pin for aligning the depressions with the terminal.